Core-shell anatase anode materials for sodium-ion batteries: the impact of oxygen vacancies and nitrogen-doped carbon coating

Biomass-Derived Carbon Materials for Electrochemical Energy Storage

The environmental impact from the waste disposal has been widely concerned around the world. The conversion of wastes to useful resources is important for the sustainable society. As a typical family of wastes, biomass materials basically composed of collagen, protein and lignin are considered as useful resources for recycle and reuse. In recent years, the development of carbon material derived from biomasses, such as plants, crops, animals and their application in electrochemical energy storage have attracted extensive attention. Through the selection of the appropriate biomass, the optimization of the activation method and the control of the pyrolysis temperatures, carbon materials with desired features, such as high-specific surface area, variable porous framework, and controllable heteroatom-doping have been fabricated. Herein, this review summarized the preparation methods, morphologies, heteroatoms doping in the plant/animal-derived carbonaceous materials, and their application as electrode materials for secondary batteries and supercapacitors, and as electrode support for lithium-sulfur batteries. The challenges and prospects for the controllable synthesis and large-scale application of biomass-derived carbonaceous materials have also been outlooked.

Morphology design and electronic configuration of MoSe2 anchored on TiO2 nanospheres for high energy density sodium-ion half/full batteries

Molybdenum selenide (MoSe2) has shown potential sodium storage properties due to its large layer spacing (0.646 nm) and high theoretical capacity and narrow band gap. However, as the anode material of sodium ion batteries (SIBs), the MoSe2's performance is not ideal, especially due to the layer agglomeration and stacking caused by volume expansion and low intrinsic conductivity. Hence, morphology design and electronic configuration of MoSe2 is proposed via building MoSe2 nanosheets and auxiliary sulfur doping on the surface of the TiO2 hollow nanosphere (S-MoSe2@TiO2). The hierarchical shaped S-MoSe2@TiO2 effectively overcomes the shortcomings of high surface energy and weak interlayer van der Waals force of MoSe2. As anode for SIBs, S-MoSe2@TiO2 delivers enhanced cycling life and rate capability (308 mAh/g at 10 A/g after 1000 cycles) with the comparison of MoSe2@TiO2 or pure MoSe2 and TiO2. Such excellent sodium storage performance is due to the fast diffusion kinetics of Na+. When it is applied in sodium ion full batteries, the S-MoSe2@TiO2 anode based cell can reach a high energy density of 187.8 W h kg-1 at 148.3 W kg-1. The design of the new MoSe2-based hybrid provides a novel scheme for the preparation of advanced anode in SIBs.

Nb-Doped TiO2 with Outstanding Na/Mg-Ion Battery Performance

The group "beyond Li-ion" batteries (Na/Mg-ion batteries) have the advantages of abundant reserves and high theoretical specific capacity. However, the sluggish kinetics resulting from large ion radius (Na⁺) and polarity (Mg²⁺) seriously limit the battery performance. Herein, we prepared Nb-doped anatase TiO₂ with Ti vacancies (Nb-TiO₂) through a simple solvothermal and subsequent calcination process. The Nb doping widens the channels for metal ion diffusion, and the cationic vacancies can act as ion storage sites and improve the electrode conductivity. Thus, Nb-TiO₂ exhibits improved performance for rechargeable Na/Mg-ion batteries.

Molecular grafting towards high-fraction active nanodots implanted in N-doped carbon for sodium dual-ion batteries

Sodium-based dual-ion batteries (Na-DIBs) show a promising potential for large-scale energy storage applications due to the merits of environmental friendliness and low cost. However, Na-DIBs are generally subject to poor rate capability and cycling stability for the lack of suitable anodes to accommodate large Na+ ions. Herein, we propose a molecular grafting strategy to in situ synthesize tin pyrophosphate nanodots implanted in N-doped carbon matrix (SnP2O7@N-C), which exhibits a high fraction of active SnP2O7 up to 95.6 wt% and a low content of N-doped carbon (4.4 wt%) as the conductive framework. As a result, this anode delivers a high specific capacity ∼400 mAh g-1 at 0.1 A g-1, excellent rate capability up to 5.0 A g-1 and excellent cycling stability with a capacity retention of 92% after 1200 cycles under a current density of 1.5 A g-1. Further, pairing this anode with an environmentally friendly KS6 graphite cathode yields a SnP2O7@N-C||KS6 Na-DIB, exhibiting an excellent rate capability up to 30 C, good fast-charge/slow-discharge performance and long-term cycling life with a capacity retention of ∼96% after 1000 cycles at 20 C. This study provides a feasible strategy to develop high-performance anodes with high-fraction active materials for Na-based energy storage applications.

Melamine-assisted synthesis of porous V2O3/N-doped carbon hollow nanospheres for efficient sodium-ion storage

Vanadium-based oxides with relatively high theoretical capacity have been regarded as promising electrode materials for boosting energy conversion and storage. However, their poor electrical conductivity usually leads to unsatisfied performance and poor cycling stability. Herein, uniform V₂O₃/N-doped carbon hollow nanospheres (V₂O₃/NC HSs) with mesoporous structures were successfully synthesized through a melamine-assisted simple hydrothermal reaction and carbonization treatment. We demonstrated that the introduction of melamine played an essential role in the construction of V₂O₃/NC HSs. Benefitting from the special mesoporous structure and large specific surface area, the as-obtained sample exhibited enhanced conductivity and structural stability. As a proof of concept, well-defined V₂O₃/NC HSs exhibited excellent cycling stability and rate performance for sodium-ion batteries, and achieved a discharge capacity of 263.8 mA h g^-1 at a current density of 1.0 A g^-1 after 1000 cycles, one of the best performances of V-based compounds. The enhanced performance could be attributed to the synergistic effect of the hollow structure and surface carbon coating. The present work describes the design of the morphology and structure of vanadium-based oxides for energy storage devices.

Cobalt-doping SnS2 nanosheets towards high-performance anodes for sodium ion batteries

Layered SnS₂ is considered as a promising anode candidate for sodium-ion batteries yet suffers from low initial coulombic efficiency, limited specific capacity and rate capability. Herein, we report a cobalt metal cation doping strategy to enhance the electrochemical performance of a SnS₂ nanosheet array anode through a facile hydrothermal method. Benefitting from this special structure and heteroatom-doping effect, this anode material displays a high initial coulombic efficiency of 57.4%, a superior discharge specific capacity as high as 1288 mA h g^-1 at 0.2 A g^-1 after 100 cycles and outstanding long-term cycling stability with a reversible capacity of 800.4 mA h g^-1 even at 2 A g^-1. These excellent performances could be ascribed to the Co-doping effect that can increase the interlayer spacing, produce rich defects, regulate the electronic environment and improve conductivity. Besides, a carbon cloth substrate can maintain the integrity of the electrode material framework and buffer its volume variation, thus boosting intrinsic dynamic properties and enhancing sodium storage performance.